The object of the present invention is an articulation for the back of a seat, which articulation is made of a first flange rigidly connected to the sitting portion of the seat and therefore fixed, and a second flange rigidly connected to the back of the seat and therefore mobile with respect to the aforementioned fixed first flange, the mobile second flange being mounted on a pin rigidly connected to the fixed first flange.
Many articulations for a seat back are already known and comprise a blockage member between the fixed portion and the mobile portion of the articulation, which blockage member is made of a single bearing plate sliding under action of a cam, this bearing plate having a lower portion which is toothed in order to cooperate with a toothing carried by a lower part of the mobile portion of the articulation.
It has however been found that such articulations with a single bearing plate exhibit a small play due to manufacturing tolerances provided for their assembly. It should also be noted that when, under an abnormal effort due to a violent impact, the single bearing plate is caused to imprint on the guiding zone and, also, the toothings of the bearing plate, which cooperate with toothings provided in the mobile portion, are caused to sag. The back of the seat is therefore not perfectly fixed any more with respect to the sitting portion, thereby reducing the comfort of the user of the seat and being a cause of possible serious accidents due to later heavy impacts.
Moreover, in order to increase comfort, ever thinner and thinner toothings have been used, and which accept only badly an imperfect engagement of the bearing plate caused either by a play due to manufacturing tolerances or by a subsiding of the material on the bearing zone of the bearing plate.